1. Field of the Invention
The present invention relates to an image forming device capable of performing transfer of paper in a highly accurate manner.
2. Description of the Prior Art
An image forming device such as a printer was conventionally provided with a stepping motor or a DC motor provided with an encoder as a driving source, and a paper transfer mechanism for transmitting rotation of the stepping motor or the DC motor to transfer rollers through gear trains and thereby transferring paper through the transfer rollers.
When a stepping motor is used as a driving source, the amount of transferring paper is controlled by controlling the amount of rotation of the motor using pulse driving. When a DC motor provided with an encoder is used as a driving source, the amount of transferring paper is controlled by controlling the amount of rotation of the DC motor using closed-loop control based on the output of the encoder.
However, the amount of transferring paper that is actually transferred, which cannot be detected by a stepping motor itself, can only be estimated based on the number of driving pulses supplied to the motor. On the other hand, the transfer accuracy of a DC motor provided with an encoder is influenced by the resolution performance of the encoder.
Therefore, improvement in detection accuracy has been desired so as to satisfy the demand these days to detect the amount of transferring paper in high accuracy, for example down to several μm.
Furthermore, it is impossible to perform highly accurate transfer of paper with the above-mentioned control mechanisms, in which the behavior of the paper is estimated based on the operation of the driving system, because of rotational pitch errors due to structures of the motor, accuracy errors of gears caused during manufacture thereof, outer diameter errors of transfer rollers and errors in transfer amounts that are dependent on the types of paper used.
The present invention has been made in view of the above points, and it is an object thereof to provide an image forming device capable of detecting the movement of a medium to be printed on in high accuracy and performing accurate transfer of the medium to be printed on.